Interfaces and Collection Classes in Delphi

Example 5: Constructing the tree view representation of the red-black tree

// Debug a red-black tree by showing the internal tree structure.
// Visibly display an image for red and black nodes. To help color-blind
// users, Red nodes have a Round icon and Black nodes have a Box icon.

// Let the debug form access protected methods and properties.
type
  TExposeTree = class(TRbTree)
  end;
  TExposeNode = class(TRbNode)
  end;

// Refresh the tree display after changing the tree.
procedure TTreeForm.RefreshTree;
  procedure WalkTree(RbNode: TRbNode; ViewNode: TTreeNode);
  var
    Item: ICollectible;
    Assoc: IAssociation;
  begin
    if RbNode <> TExposeTree(Tree).Leaf then
    begin
      // Get the string item from the node. If the collection is a map,
      // the node holds an association, and the string is the key.
      Item := TExposeNode(RbNode).Item;
      if Item.QueryInterface(IAssociation, Assoc) = S_OK then
        Assoc.GetKey(Item);
      ViewNode := TreeView.Items.AddChild(ViewNode, (Item as IString).Value);
      if TExposeNode(RbNode).IsRed then
        ViewNode.ImageIndex := 0
      else
        ViewNode.ImageIndex := 1;
      ViewNode.SelectedIndex := ViewNode.ImageIndex;

      WalkTree(TExposeNode(RbNode).Left, ViewNode);
      WalkTree(TExposeNode(RbNode).Right, ViewNode);
    end;
  end;
  
begin
  TreeView.Items.BeginUpdate;
  try
    TreeView.Items.Clear;
    WalkTree(TExposeTree(Tree).Root, nil);
    TreeView.FullExpand;
  finally
    TreeView.Items.EndUpdate;
  end;
end;